[R] Non-linear regression/Quantile regression

[Greg Snow]

poly by default uses orthogonal polynomials which work better mathematically but are harder to interpret.  See ?poly
 
-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of despaired
> Sent: Tuesday, June 09, 2009 9:59 AM
> To: r-help at r-project.org
> Subject: Re: [R] Non-linear regression/Quantile regression
> 
> 
> Hi,
> 
> thanks, it works :-)
> But where is the difference between demand ~ Time + I(Time^2) and
> demand ~
> poly(Time, 2) ?
> Or: How do I have to interpret the results? (I get different results
> for the
> two methods)
> 
> Thank you again!
> 
> 
> Gabor Grothendieck wrote:
> >
> > Those are linear in the coefficients so try these:
> >
> > library(quantreg)
> >
> > rq1 <- rq(demand ~ Time + I(Time^2), data = BOD, tau= 1:3/4); rq1
> >
> > # or
> > rq2 <- rq(demand ~ poly(Time, 2), data = BOD, tau = 1:3/4); rq2
> >
> >
> > On Tue, Jun 9, 2009 at 10:55 AM, despaired<meyfarth at uni-potsdam.de>
> wrote:
> >>
> >> Hi,
> >>
> >> I'm relatively new to R and need to do a quantile regression. Linear
> >> quantile regression works, but for my data I need some quadratic
> >> function.
> >> So I guess, I have to use a nonlinear quantile regression. I tried
> the
> >> example on the help page for nlrq with my data and it worked. But
> the
> >> example there was with a SSlogis model. Trying to write
> >>
> >> dat.nlrq <- nlrq(BM ~ I(Regen100^2), data=dat, tau=0.25, trace=TRUE)
> >>
> >> or
> >>
> >> dat.nlrq <- nlrq(BM ~ poly(Regen100^2), data=dat, tau=0.25,
> trace=TRUE)
> >>
> >> (I don't know the difference) both gave me the following error
> message:
> >>
> >> error in getInitial.default(func, data, mCall =
> as.list(match.call(func,
> >>  :
> >>  no 'getInitial' method found for "function" objects
> >>
> >> Looking in getInitial, it must have to do something with the
> starting
> >> parameters or selfStart model. But I have no idea, what this is and
> how I
> >> handle this problem. Can anyone please help?
> >>
> >> Thanks a lot in advance!
> >> --
> >> View this message in context:
> >> http://www.nabble.com/Non-linear-regression-Quantile-regression-
> tp23944530p23944530.html
> >> Sent from the R help mailing list archive at Nabble.com.
> >>
> >> ______________________________________________
> >> R-help at r-project.org mailing list
> >> https://stat.ethz.ch/mailman/listinfo/r-help
> >> PLEASE do read the posting guide
> >> http://www.R-project.org/posting-guide.html
> >> and provide commented, minimal, self-contained, reproducible code.
> >>
> >
> > ______________________________________________
> > R-help at r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide
> > http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
> >
> >
> 
> --
> View this message in context: http://www.nabble.com/Non-linear-
> regression-Quantile-regression-tp23944530p23945900.html
> Sent from the R help mailing list archive at Nabble.com.
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-
> guide.html
> and provide commented, minimal, self-contained, reproducible code.